Except as provided in Chapters 3 (§ 58.1-300 et seq.) and 6 (§ 58.1-600 et seq.) of this title, any tax imposed by this subtitle shall be assessed within three years from the last day prescribed by law for the timely filing of the return. In the case of a false or fraudulent return with the intent to evade payment of any tax imposed by this subtitle, or a failure to file a required return, the taxes may be assessed, or a proceeding in court for the collection of such taxes may be begun without assessment, at any time within six years from the last day prescribed by law for the timely filing of the return.